1. Field of the Invention
The present invention relates to a method of producing an optical element using a garnet single crystal.
2. Description of the Related Art
Faraday rotator is an optical element with a function to rotate the polarization plane of transmitting light and is used in optical devices such as optical isolator and optical circulator for communication. Faraday rotator is generally prepared by using a plane-like bismuth (Bi)-substituted rare-earth iron garnet single crystal. The Bi-substituted rare-earth iron garnet single crystal is prepared by the liquid phase epitaxial (LPE) process as one of flux processes.
In growing the Bi-substituted rare-earth iron garnet single crystal by the LPE process, generally, lead oxide (PbO), bismuth oxide (Bi2O3) and boron oxide (B2O3) are used as the solvents so as to stably grow the garnet single crystal while the solvents are maintained at the supersaturation states. During the growth of the magnetic garnet single crystal, therefore, a small amount of lead (Pb) contaminates in the resulting crystal. In Faraday rotators for use in optical devices for communication, magnetic garnet single crystals at a Pb content “y” of about 0.03 to 0.06 in the chemical formula Bi3-x-yM1xPbyFe5-z-wM2zM3wO12 have been used conventionally. See Patent Reference 1: the official gazette of JP-A-2001-044026 and Patent Reference 2: the official gazette of JP-A-2001-044027.
Following the upsurge in the recent environmental protection movement, however, efforts are now directed toward the reduction of the content of Pb as an environmental load substance in any of industrial products. Therefore, a trace amount of contaminating Pb in magnetic garnet single crystals grown by the LPE process draws concerns as a factor of environmental pollution. Therefore, it is necessary to reduce or eliminate the amount of Pb contained in magnetic garnet single crystals as materials constituting optical elements as such Faraday rotators.